Local Biological Indicators
Biological conditions experienced by juvenile salmon entering the northern California Current.
Copepod Biodiversity
Copepods drift with the ocean currents, making them good indicators of the origins of water transported into the northern California Current (NCC). Copepod biodiversity (or species richness) measures the number of copepod species in a plankton sample. We can use species richness to index the types of water masses present in Oregon and Washington's coastal zone.
Off the Oregon and Washington coasts, species richness is low in the summer when sub-Arctic waters dominate, containing zooplankton assemblages of low diversity (Figure CB-01; Hooff and Peterson, 2006). Alternatively, coastal waters are fed by the poleward flowing Davidson Current during the winter. The current brings a highly diverse assemblage of subtropical copepods to the NCC.
We use the monthly copepod richness anomaly (seasonal cycle removed) to index the biological response to climatological indices (Figure CB-02). Although copepod richness changes seasonally, basin-wide processes, indexed by climatological indices such as the PDO and ENSO, can also influence the copepod species richness in coastal waters. During negative (cool) periods of the PDO, species richness is low, and during warm events, when the PDO is positive (warm) or during El Niño events, species richness is high (Hooff and Peterson, 2006).
Measuring copepod species richness over time can help us track whether climate change is impacting biodiversity. In 2009, we reported species richness had increased over the previous 40 years, at a rate of 4.4 species per year. While this increase in biodiversity over this time period may be due to warming waters associated with climate change, there are clear strong events that may be driving this pattern. Figure CB-04 shows the winter and summer species richness since 1969 and from 1996-present. There is a general trend of increasing species richness since the beginning of the time series until 2018. However, species richness since 2020 has decreased back to levels similar to those in the mid 1990s.


